Since polyester has excellent mechanical strength, chemical stability and transparency, as well as being inexpensive, it is one of the synthetic resins most commonly used as a fibrous material throughout the world. Of all kinds of polyester, polyethylene terephthalate (PET) is particularly advantageously used because of its excellence in general versatility and practical applicability.
Generally speaking, polyethylene terephthalate is manufactured from terephthalic acid or an ester-forming derivative thereof, and ethylene glycol. Such raw materials are normally obtained from fossil resources. Although oil, a fossil resource, is an important raw material in the chemical industry, it is a cause of global warming and other environmental problems as it generates large quantities of carbon dioxide during manufacturing and incineration disposal, not to mention concerns over future depletion. Such being the case, much attention has been focused on reclaimed materials and materials with a low environmental load.
Biomass resources are produced by plants from water and carbon dioxide through photosynthesis, and take the forms of starch, carbohydrate, cellulose, lignin, and the like. Since biomass resources take in carbon dioxide as one of their input materials during their formation processes, any material that uses a biomass resource does not produce any net carbon dioxide emissions in its life cycle, even if it is decomposed into carbon dioxide and water during post-use incineration disposal. As this carbon dioxide may, under certain circumstances, be recycled by plants, biomass resources can be regarded as renewable resources. Accordingly, using such biomass resources as an alternative to oil resources helps preserve fossil resources and reduce carbon dioxide emissions.
Against this background, ways to synthesize polyester, a very high-demand polymer in the world, from renewable biomass resources are being studied. Examples include a report on PET synthesized from biomass-derived ethylene glycol (Chinese Patent Publication No. 101046007). However, since biomass-derived ethylene glycol is low in purity, any polymer obtained from it exhibits a problem of thermostability in the form of a low melting point.
As a method to overcome this problem, an adsorption treatment designed to remove impurities from biomass-derived glycol using activated carbon has been disclosed (Japanese Unexamined Patent Publication (Kokai) No. 2009-209145). That method has made it possible to obtain polymers with melting points comparable to those synthesized from fossil resource-based glycols.
Compared to fossil resource-based polymers, polymers synthesized from biomass-derived glycol still have poor thermostability. Usually, polyester chips are subjected to the processes of remelting and molding into a filament, a film, and a resin. In this commonly performed processes, exposure of polymers synthesized from biomass-derived glycol to a temperature approaching 300° C. promotes their decomposition reaction, resulting in yellowing, a reduction in viscosity, and a reduction in molecular weight, leading to undesirable phenomena in use, including an increased soiling of the die of the molding machine, generation of foreign matter, and a reduction in physical properties of a resin molded article. In particular, an artificial leather comprising an ultrafine fiber, and the like are remarkably affected.
Accordingly, the development of a polyester having excellent thermostability during melt molding and imparting favorable physical properties to an application product, namely a polyester ultrafine fiber which exhibits only a small reduction in intrinsic viscosity during melt molding and can impart excellent abrasion characteristics to the product, as well as a base body for an artificial leather using the polyester ultrafine fiber has been desired.
It could therefore be helpful to provide a base body for an artificial leather comprising a polyester excellent in thermostability during melt molding. That is, it could be helpful to provide an ultrafine fiber comprising a polyester which exhibits only a small reduction in intrinsic viscosity during melt molding and can impart excellent abrasion characteristics to the product, as well as a base body for an artificial leather using the ultrafine fiber.